When a pupil plays her flute in the classroom the window vibrates give the reason for this?

Everything in the room vibrates with every sound. It just happens that the only thing you notice is the window. If it only happens at certain notes it is called resonance. If it keeps rattling after the note ends it is called reverberation.

A xylophone has wood blocks that produce the notes. Sometimes each block has a tube of exact length to resonate at that note. A tube open at both ends will resonate with even multiples of the note, and a tube closed at one end will resonate with odd multiples, so a vibraphone has a flapper that is rotated to open and close the tubes and that gives a unique character to the sound. Like this: www.youtube.com/watch?v=pAGKfaTZakQ
xylophone with open tubes: www.youtube.com/watch?v=2eOnm2tYJHs
Xylophone without tubes: www.youtube.com/watch?v=ITc6FsXsVhs